A generation of a knock event in a engine is a considerable problem, because when an engine knocks it can also cause severe damages on the engine. In an internal combustion engine the air and fuel mixture is introduced into a combustion chamber and then compressed by an ascending movement of a piston, the compressed mixture is fired and combusted by a spark that is generated by applying a high voltage to a spark plug installed in the combustion chamber and the force produced as the piston is pushed down is recovered as work. Occasionally the pressure created by the combustion itself can cause the air and fuel mixture not yet combusted to ignite prematurely, creating a smaller, instantaneous combustion of the end gas that is the cause of the knock event. This condition is not desirable because it can damage or destroy engine parts so it is desirable to prevent the generation of knock event. When combustion is performed in the combustion chamber, molecules of the mixture in the chamber are ionized, so when a measuring voltage is impressed to the spark plug in the combustion chamber, a current, ion current, flows due to the electric charge of the ions. It is known that the ion current changes depending on the combustion pressure and hence, occurrence of a knock (pressure oscillation) can be determined by detecting the signal content of the ion current.
U.S. Pat. No. 6,439,029 discloses a method of detecting an occurrence of a knock event in an internal combustion engine by detecting an ion current from initiation of combustion in a cylinder and judging a knock component overlapping the ion current based on a judging level. This method is, however, not sufficiently accurate if the operation of the engine fluctuates, for example when the engine is exposed to strains or if a new fuel mixture is used. It is hard to get a reliable analysis through this known technique.
U.S. Pat. No. 6,185,984 discloses a device that detects the ion current and then uses algorithms on the filtered signals to judge if a knock event has arisen. This method, however, also lacks the stability needed to yield sufficient results with regards to a knock event at small signal levels normally encountered in lean burn engines.
U.S. Pat. No. 4,565,087 discloses a method and device for detecting a knock event in an internal combustion engine. The method, however, does not take into account the effect of alterations in fuel concentration, or indeed changing fuel altogether, which would result in a different levels of ion current, rendering the detection of a knock event difficult.
Therefore it is obvious that there is a need to find a solution to the above mentioned problems.